Well there are plenty of bows that require dexterity. I can't remember if any armor requires dex. I think it's either strength or intelligence. Pretty much, if you look at the loot you get now - it'll be the same later on, just with more advanced stats and requirements. You won't suddenly see a bow requiring strength, for example, or a sword requiring dex.
564 damage is nice, though I believe the actual number is higher. The only advantage fireball has over explosive arrows is that you can get it earlier. Even if the damage for one fireball is higher than that of an explosive arrow - the fact that can you can fire several explosive arrows, in the time it takes fireball to cool down, makes that a non issue.
I remember doing upwards of 2000 damage with explosive arrows :> Some creatures are more resistant to it than others though, just like with fireball.
